Spark-plug.



F. M. FURBER.

SPARK PLUG.

APPLICATION FILED FEB. 5. 1915.

Patented June 13, 1916.

MTA/5555.

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FREDERICK M. FURBEIB., OF REVER. MASSACHUSETTS.

- SPARK-PLUG..

Specification of Letters Patent.

Patented June 13, 1916.

Application led February 5, 1915. Serial No. 6,365.

To all whom t may opncern Be it known that I, FREDERICK'M. FURBER, a citizen ofthe United States, residing at Revere, in the county of Suffolk and State of Massachusetts, have invented certain new and useful Improvements in Spark-Plugs, of which the following' description, in connection with the accompanying drawings, is a specification, like reference characters on the drawings indicating like parts in the several figures.

lThis invention relates to spark plugs of the character commonly used in internal combustion engines.

The invention aims to improve the construction and methods of manufacture of spark plugs with a view particularly to reducing the manufacturing cost of devices of this character while producing a substantial and serviceable plug.

The invention is particularly concerned with the mounting of the insulator in the body or outer shell of the plug and provides a very simple construction by which a gas tight joint between the insulator and the body is produced and in which the breakage of insulators due to sudden and severe changes in temperature is substantially eliminated.

The invention will be readily understood from the following description, reference being made to the accompanying drawings, in which- 1 Figure 1 is a view in side elevation of a plug constructed in accordance with the invention; Fig. 2 is a central, vertical, sectional view of the plug shown in Fig. l; Fig. 3 is a view similar to Fig. 2 of a slightly modified construction; Fig. 4 is a view similar to Fig. 2 of another modification; and Fig. 5 is a cross-sectional view on the line A-A, Fig. 4.

Referring now to the drawings, 2 indicates the body or outer shell of the plug, which preferably is made from bar stock of Vhexagonal cross-section by turning off the free end of the collar 6. Since the threaded end 4 of the plug is designed to be secured` in the cylinder of an engine, this end may be referred to as the inner end of the plug and the opposite end as the outer end. The tapered surface in the free portion of the collar 6, that is, the portion above the thick part of the body 2, forms the seat for the insulator. It will be evident that this body can be made automatically in a turret lathe, all the operations being performed before the body is severed from the bar from which it is made, thus requiring but a single handling of this part of the plug.

The insulator'` 1,0 has a tapered surface 12 formedthereon designed to fit the tapered 'seat in the collar 6. These tapers are very gradual and are sometimes designated as sticking tapers.

In using some kinds of insulators, particularly those made of the cheaper grades of porcelain, the surface of the insulators -may be molded so roughly that it will be tapered part 12 of the insulator with suii- I cient pressure to hold the insulator very securely in the body. It will be noted that the tapered surface 12 on the insulator is 'short and that it is in engagement only with the free portion of the collar. This collar is made so thin that it cannot eXert sufficient pressure on the insulator to crush it and yet is made thick enough to enable it to grip the insulator firmly and to afford a very substantial support for the insulator. I have found that, when cold rolled stock, which is very commonly employed for spark plug shells or bodies, is used, very satisfactory results are obtained when the collar' 6 is made from one thirty-second to one sixteenth of an inch thickf In order to be sure to have the temperature of-the collar 6 sufficiently high when the insulator is inserted in the body, I prefer to heat it to such a point that the collar 6 begins to glow; although satis- It will be noted that, in the construction shown, the part of the insulator 10 below `the tapered portion 12 is substantially smaller in diameter than the diameter of the bore of the body 2 and consequently is out of contact with the body. This arrangement has two advantages; rst, that it prevents the body from gripping the insulator at any point where it has sufl'icient metal to seize the insulator with pressure enough to break it; and second, that it permits the use of an insulator having a very long leakage surface inside the body and consequently redllices the liability of short circuiting the u l P 1% is obvious that the insulator might be mounted in the collar 6 by forcing it into the body and thus causing the collar 6 to grip the tapered portion l2 of the insulator with sufficient pressure to hold it in the plug but I prefer the method above desci'ibed because it produces an entirely satisfactory article without the use of presses which otherwise would be required. This method also has the advantage f bringing the collar 6 to such a physical condition that, when it shrinks, it will conform to the minor differences in shape between the tapered surface 12and the seat in the collar and thus will insure a gas tight joint between the insulator and the body. Since, according to the preferred method, the collar is heated to a higher temperature than it will ever attain in use, there is no danger of the collar ever expanding .suiciently to release the insulator. The strains placed upon the"in sulator due to changes in temperature while it is in use will be less than those to which it is subjected in manufacture since the changes in temperature will be less severe and the liability of breakage of insulators due to this cause thus is avoided. AThe extreme simplicity in construction of the plug and the fact that very few operations and very little machinery are required in its manufacture,

enable the plug to be manufactured at a very small cost.

The particular shape and dimensions of the insulator employed andthe arrangement of electrodes and terminals may vary with the requirements of particular cases. Inthe specific construction shown, the insulator is provided with a small central bore in which an electrode stem 14 is fitted, this stem being turned over at right angles near the lower end of the insulator to form an electrode 16 which is separated from the'.

.inner wall of the body by a spark gap so .-that the body itself constitutes one of the electrodes. Theupper end of the stem 14 is headed over the` top of the insulator and crimped over a circumferential shoulder formed on the insulator near its upper end. This cap has an integral threaded extension 20 to receive a binding nut 22 by which the conductor carrying current to the plug can be clamped in its operative position.

The construction shown in Fig. 3 is like that shown in Fig. 2 in all substantial particulars but in this case the collar 6 has been formed by running a tool into the outer end of the body 2, thus leaving a longer hexagonal part of the body than in the construction shown in Fi 2. The insulator is mounted in the b y by shrinking the' collar 6 on to it in the manner above described.

In the modiication shown in Figs. 4 and 5, the body 2 is constructed as in Fig. 2

and the insulator is mounted in the body in the manner above described but the metal near the base of the collar at points diametrically opposite each other has been punched inwardly as indicated at 6 forming two internal projections that engage the insulator just below its tapered surface 12. These projections positively prevent any inward movement ofthe insulator. This construction may be used if for any reason it is desired to avoid the use of as h1 h lthe bore in said collar being constructed and shaped to form a seat for an insulator, and an insulator supported in said body and having a part fitting said seat, said collar gripping said insulator and serving solely `through its frictional engagement with said insulator to support it in operative position in said body.

2. In a spark plug, a body, an insulator supported in said body, and a thin collar integral with said body and shrunk on to the insulator and supporting the insulator in the body solely through its frictional engagement with the insulator. y

3. In a spark plug, a body and an insulator supported in said bod said body having at its outer end a thin collar formed integrally therewith, said collar ripping said insulator and serving as the so e means for holding the insulator m the body...

4. In a spark plug, a body and-an insulator supported in sald body, said body having formed inte rally therewith a thm'collar, and said co ar being shrunk on to said insulator and serving as the sole means for supporting the insulator in the body.

5. A spark plug, a body having a. thin collar projecting from its upper end and aormedintegrally therewith, said body hav- Ylng a boe extending therethrough vand through said collar, the part ofthe bore in said collar being gradually tapered toward the outer end of the collar, and an insulator having a tapered seat itting in thetapered bore of said collar, said collar being shrunk on to said insulator and said insulator being free from contact with said body at other points. f

6. In a spark plug, a body, a thin collar integral with said body and having a part free from contact with the body, and an insulator supported in said body solely by the free portion of said collar.

7. In a spark plug, a body, an insulator supported in said body, a collar projecting from said body but integral therewith and shrunk on to the insulator, said collar serving as the sole means for supporting the insulator in the body and being of. such a thickness as to grip the insulator with suicient firmness to hold it securely in the body but incapable of exerting suiicient pressure on the insulator to crush it.

8. In a spark plug, a body having a thin collar projecting therefrom, said collar being constructed and shaped to form a seat for an insulator, and an insulator supported in said seat, said colla;` gripping said insulator and operating solely through its engagement therewith to support the insulator in said body and being of such a thickness as to hold the insulator securely but incapable of exerting sufficient pressure on the insulator to crush it.

In testimony whereof I have aixed my signature, in presence of two witnesses.

FREDERICK M. FURBER.

I Witnesses:

ARTHUR F. RAY, J. H. MCCREADY.

Pitent-.NomSagesse? It is hereby certified that in Letters Patent No. 1,186,568, granted June 13, M316,

upon the application of Frederick M. Furber, of Revere, -Massachusettafor an improvement in Spark-Plugs, an errorappears in the printed speciica'tion l correctie# as follows: Page 2, line 1301 claim 5" for -the'wmds A sI/)ark read In'aI spark plug; and that the said Letters Patent'should be read correction therein thatftheeame may conform tolthe record of the case the Patent Oflice. -V 'signednd miga this sth day f Angst', A. D., 19mg Y [sain] 

